Tracking control apparatus for use in apparatus for reproducing video signals from a rotary recording medium

ABSTRACT

A tracking control apparatus is employed in apparatus for reproducing video signals from a rotary recording medium. A reproducing transducer is used for reproducing recorded signals in which a main information signal has been recorded in a plurality of adjacent tracks and at least one reference signal has been recorded at an intermediate position between the longitudinal center lines of the adjacent tracks. The tracking control apparatus positions the reproducing transducer to follow a correct tracking along the main information signal track. The reference signal is separated from the signal reproduced by the reproducing transducer. A control signal is produced in response to the separated reference signal for application to the tracking control means. An automatic gain control operation fixes the level of the separated reference signal at a stage prior to the stage where the control signal is produced.

BACKGROUND OF THE INVENTION

The present invention relates generally to tracking control apparatusfor reproducing recorded signals from rotary recording mediums. Moreparticularly, the invention utilizes a main information signal and pilotsignals for controlling tracking by the reproducing transducer whichmoves accurately and stably over the main information signal track ofthe recording medium.

Known systems record and reproduce information signals (such as videosignals and/or audio signals) on and from disc-shaped, rotary mediums(referred to hereinafter simply as discs). These are broadly dividedinto systems using optical reproduction, systems using a reproducingstylus employing a piezoelectric element, and systems utilizingvariations in the electrostatic capacitance between an electrode on thereproducing stylus and the recorded surface of the disc.

The advantages and disadvantages of these three kinds of systems havebeen considered. It is concluded that the electrostatic capacitancesystem is most desirable. Further, the present applicant has previouslydescribed, as a new system for overcoming the problems accompanyingknown electrostatic capacitance system, a novel "Information signalrecording system" as disclosed in the specification of U.S. patentapplication Ser. No. 785,095, filed Apr. 6, 1977.

More particularly, in accordance with a known electrostatic capacitancesystem, recording is accomplished by forming a spiral guide groove inthe disc for guiding the reproducing stylus. At the same time, pits areformed in responsive correspondence with an information signal to berecorded on the bottom surface of the groove. In the reproducing system,the reproducing stylus is guided by the guide groove. The stylus tracesthe track within the groove and reproduces the signal in response tovariations in the electrostatic capacitance.

In this known system, however, a reproducing stylus guiding groove isprovided in the disc. The reproducing stylus is compulsorily guided bythis guide groove. It is not possible for the reproducing stylus toundergo operations such as riding over the groove wall of one track,moving into another track and returning to the original track. If thereproducing stylus were to be forced to undergo such an operation, thegroove and the stylus would be damaged. For this reason, it has not beenpossible in this known system to carry out special reproduction such asquick-motion picture reproduction, slow-motion picture reproduction, andstill-picture reproduction.

Furthermore, since the area of contact between the tip of thereproducing stylus and the guide groove of the disc is small, the styluseasily wears. When the width of the stylus tip reaches the groove widthas a result of abrasive wear, the serviceable life of this reproducingstylus ends. Thus, this system is accompanied by the problem of shortlife of the reproducing stylus. Another problem is that fine chipparticles abrade from the disc by the tracing action of the reproducingstylus along the guide groove. These chips give rise to difficultieswhich promote the wear and damage of the stylus and the guide groove.This wear increases the gap between the electrode at the stylus tip andthe recorded surface including the pits within the disc guide groove.The reproduced output decreases because of this spacing loss.

If the rotational speed of the disc is set at a low value such as 450rpm., for example, it will prolong the life of the stylus tip. However,wavelength of the information signal recorded in the guide groove willbecome short. For this reason, a low price recording apparatus cannotemploy laser light in the recording system. The disadvantageous highprice of a recording apparatus using an electron beam becomesunavoidable.

Accordingly, an aim of the invention is to overcome the various problemsof the known systems described above. The present inventor has describedin the aforecited patent application a novel system for recording andreproducing information signals. According to this proposed system, therecording system forms pits in accordance with the information signalbeing recorded along a spiral track on a flat disc shaped recordingmedium, without forming a groove therein. In the reproducing system, areproducing stylus traces over and along this track to reproduce therecorded information signal. In this system, pilot or reference signalsare recorded on or in the vicinity of a track of the information signal,such as a video signal, on a rotary disc. At the time of reproducing,the reference signals are reproduced together with the video signal.Tracking servo control is carried out so that the reproducing stylustraces accurately along the track in response to the reproducedreference signals.

By the use of this previously described system, the recording track hasno groove. There is no possibility whatsoever of the reproducing stylusor the recording medium being damaged. The stylus can trace the sameportion of the track repeatedly many times, whereby a specialreproduction such as still, slow motion, or quick motion reproductionbecomes possible. Furthermore, other difficulties of the known systemare removed.

Furthermore, a reproducing stylus of highly desirable characteristicsmay be used for reproducing an information signal recorded on a discwithout a reproducing stylus guide groove. The present inventor haspreviously described a novel "Stylus for reproducing information signalsrecorded on a recording medium" as disclosed in the specification ofU.S. .[.patent application Ser. No. 852,366.]. .Iadd.Pat. No.4,199,782.Iaddend.. This proposed reproducing stylus has a bottomsurface with a maximum width portion which is greater than the trackpitch and has an electrode of a width smaller than the track pitch overa specific distance from the stylus tip.

A feature of this proposed reproducing stylus is that the styluspressure per unit area is small. There is a low rate of abrasive wear ofthe reproducing stylus and the disc. Another feature of this stylus isthat, the electrode width does not increase appreciably even when thestylus tip becomes somewhat worn after a long period of use. The life ofthe reproducing stylus is remarkably long.

Thus, by using the recording and reproducing system and the reproducingstylus according to the above cited applications, the problemsencountered in the prior art are overcome. Very good results can beobtained.

In the above mentioned recording and reproducing systems, two pilotsignals of mutually different frequencies are recorded on the oppositesides of each track carrying the main information signal. When thetracking of the reproducing stylus deviates relative to the maininformation signal track of the recording medium, and reproducing stylusreproduces a pilot signal together with the main information signal. Thetracking control circuit operates in response to the pilot signal toproduce an output tracking error signal corresponding to the directionand magnitude of the tracking deviation. The reproducing stylus iscontrolled in response to this error signal so as to track accuratelyover and along the main information signal track.

However, the level of the reproduced signal varies with the radialpositional displacement of the reproducing stylus on the rotaryrecording medium. The reproduced level also depends upon variation inthe contact between the electrode of the reproducing stylus and thesurface of the rotary recording medium, dust and grime adhering to thesurface of the rotary recording medium, and undesirable abrasive wear ofthe electrode part of the reproducing stylus.

Where there is a fluctuation of this nature in the level of thereproduced signal, the level of the reproduced pilot signal alsofluctuates. However, a DC error voltage is obtained in response to thefluctuating level of the reproduced pilot signal. This error voltage isapplied to the mechanism for controlling the tracking stylus, but theloop gain of the control circuit always varies together with variationof the level of the reproduced signal. In this case, the control loop isdisrupted, and stable tracking control is not attainable, wherebyerroneous tracking may occur.

SUMMARY OF THE INVENTION

Accordingly, it is a general object of the present invention to providea novel and useful tracking control device in an apparatus forreproducing rotary recording mediums in which the above describedproblem has been solved.

Another and specific object of the invention is to provide a trackingcontrol device in an apparatus for reproducing rotary recording mediums.Here, an object is to provide a device which is capable of carrying outtracking control continually, in a stable manner, irrespective offluctuations in the level of the reproduced signal.

Still another object of the invention is to provide a tracking controldevice in an apparatus for reproducing rotary recording mediums. Here,an object is to carry out special reproduction operations, such as stillreproduction wherein the same portion of the track is reproducedrepeatedly a plurality of times, slow-motion reproduction, andquick-motion reproduction wherein tracks are skipped over, by the use ofthe tracking control device.

Other objects and further features of the invention will become apparentfrom the following detailed description when read in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a block diagram of one example of an apparatus for recordingsignals on a rotary recording medium to be reproduced by a rotaryrecording medium reproducing apparatus using the tracking control deviceaccording to the invention;

FIGS. 2(A) through 2(D) are signal waveform diagrams respectively fordescribing the operation of the recording apparatus shown in FIG. 1;

FIGS. 3A and 3B are fragmentary plan views respectively showing insuccessive enlargements examplary track patterns recorded on a rotaryrecording medium, by the recording apparatus illustrated in FIG. 1;

FIG. 4 is a greatly enlarged perspective view showing a reproducingstylus tracking the information signal recording medium shown in FIGS.3A and 3B;

FIG. 5 is a block diagram of one embodiment of the tracking controlapparatus according to the invention in a reproducing apparatus;

FIG. 6 is a perspective view of one example of a reproducing transducerhaving a tracking control mechanism;

FIGS. 7(A) through 7(E) are signal waveform diagrams for a descriptionof the operation of the apparatus shown in FIG. 5;

FIG. 8 is a circuit diagram showing one embodiment of a specificautomatic gain control circuit in the apparatus shown in FIG. 5;

FIGS. 9 and 10 are block diagrams respectively showing modified examplesof an essential part of the apparatus shown in FIG. 5; and

FIGS. 11(A) through 11(D) are signal waveform diagrams for describingstill reproduction and slow-motion reproduction.

DETAILED DESCRIPTION

FIG. 1 shows one example of an apparatus for recording a signal on arotary recording medium. A laser light beam is emitted from a laserlight source 11 and is reflected by a mirror 12 through a lightmodulator 13 for adjustment of the light quantity. The adjusted lightbeam is projected onto a half mirror 14, which transmits one part of thelight to a light modulator 15 and reflects another part thereof toanother light modulator 16.

Information signals which are to be recorded such as a color videosignal and a frequency modulated audio signal, are supplied throughinput terminals 17 and 18 to an adder 19. The color video signal isindicated in FIG. 2(A) with a unit of a vertical synchronizing pulse 40,and in FIG. 2(D) with a unit of the horizontal synchronizing pulse 41.Frequency modulator 20 modulates the added output of the adder 19 on acarrier wave. The resulting frequency-modulated signal is supplied as amain information signal to the light modulator 15 which modulates thelight beam transmitted through the half mirror 14. Thefrequency-modulated signal has a carrier wave center frequency of 7.0MHz and has a frequency deviation width of 2.2 MHz. The resulting outputis projected as a first modulated light beam onto a mirror 22. There itis reflected through a polarizing prism 23 to a mirror 24, and anobjective lens 25. The beam brought to a focus on a photosensitive agentcoating an original recording disc 26 made of material such as glass.

On the other hand, a reference oscillator 27 produces an output signalof 3.58 MHz synchronized with a color subcarrier of the color videosignal. This output signal is frequency divided by 1/5 and 1/7, forexample, at frequency dividers 28 and 29, respectively. These dividedfrequencies are reference signals (hereinafter referred to as pilotsignals) for tracking control of a frequency fp1 (of 716 KHz) and afrequency fp2 (of 511 KHz). The signal from the oscillator 27 isfrequency divided by 1/13 into a pilot signal of frequency fp3.Accordingly, the pilot signals of frequencies fp1, fp2 and fp3 exist ina frequency band which is lower than the frequency band of the frequencymodulated information signal.

In the present embodiment of the invention, a video signal of two frames(4 fields) is recorded for every revolution of the original disc 26. Theswitching circuit 30 operates in the following manner. In a certaintwo-frame period as indicated in FIG. 2(B), the pilot signal fp1 fromthe frequency divider 28 is in phase synchronism with the horizontalblanking period for every period H (horizontal scanning period), asindicated in FIG. 2(D). In the succeeding 2-frame period, the pilotsignal fp2 is obtained from the frequency divider 29 in phasesynchronism with the horizontal blanking period, for every period H.This operation is repeated thereafter. Furthermore, the pilot signal fp3is obtained from the frequency divider 36 is obtained in phasesynchronism with the vertical blanking period every two frames. Theoutput pilot signals from the switching circuits 30 are supplied to thelight modulator 16. In a modification, the pilot signal of frequencyfp3, from the switching circuit 30, is not supplied to the lightmodulator 16. It may be supplied through terminals 37a and 37b, to anadder 21 in which it is added to the frequency modulated maininformation signal from the frequency modulator 20. In thismodification, the pilot signal of frequency fp3 is recorded at positionscorresponding to the vertical blanking periods in the main informationsignal track.

The light beam reflected by the half mirror 14 is modulated in the lightmodulator 16 by the pilot signals. The resulting output is reflected bya mirror 31 as a second modulated light beam. The beam is introducedinto the polarizing prism 23, where its polarization plane is angularlyshifted by 90 degrees from that of the first modulated light beam. Thesecond modulated light beam leaves the polarizing prism 23, togetherwith the first modulated light beam. They are reflected by the mirror24, through the objective lens 25, and focused onto the originalrecording disc 26.

The original disc 26 is mounted on a turntable 32, and rotated at aspeed of, for example 900 rpm., by a motor 33. The origial disc 26,turntable 32, and motor 33 are unitarily and continuously transported ata specific pitch in the arrow direction X, by means of a transportingmechanism (not shown). As a result, the main information signal and thepilot signals are recorded on the original disc along a spiral trackprogressing from its outer periphery toward its central part. Thesesignals are respectively recorded by the first and second modulatedlight beams.

Furthermore, a displacement position detector 34 comprises apotentiometer which detects the displacement position due to thetransporting movement of the original disc 16 and the turntable 32, asthey are transported in the arrow direction X. The potentiometerproduces an output DC voltage which varies responsive to thedisplacement position. This detected DC voltage is passed through a DCamplifier 35 to light modulator 13. The light quantity is adjusted tocontrol the intensity of the beam from the laser light source 11 inaccordance with the radial position of the light beam spot focused onthe disc 26. This arrangement and operation compensates to eliminate theeffect of any difference in the relative linear speed due to theshifting position of the light beam spot along the radial direction asthe track spirals in toward the center of the original disc 26.

The original disc 26 is exposed to light in the above described mannerand subjected to a known developing process and to a known discfabricating process. A completed recorded disc is thus obtained. Therecorded disc comprises, for example, a disc substrate made of polyvinylacetate (PVAC), in which the pits are formed along a spiral track. Ametal electrode coating is formed with a thickness of 400 A, forexample, on the disc substrate, and a dielectric coating film of athickness of 400 A is adhered onto the metal coating. The disc may begiven an electrode function by using another material instead of a metalcoating film.

It is to be observed that an electron beam may be used in place of alaser light beam in the above described apparatus. Furthermore, insteadof the arrangement wherein the original disc, turntable 32, and motor 33are transported in the arrow direction X, an arrangement may be providedwherein an optical system projects the light beams onto the originaldisc 26 with the beam being transported in the direction opposite to thearrow direction X.

One embodiment of the disc, according to the invention, which isobtained by the recording apparatus illustrated in FIG. 1, will now bedescribed with reference to FIGS. 3A and 3B. In FIG. 3A, the recordeddisc 50 has a track formed in a spiral path. One portion within itscircular shape is shown enlarged in FIG. 3B. In FIG. 3B, successiveturns of the single continuous spiral track, on the disc 50 aredesignated as t₁, t₂, t₃ . . . . Each track segment is constituted bythe formation of pits 51 of the main information signal. With respect toone track t₁, during every period H, at a position (H.BLK) correspondingto the horizontal blanking period, pits 52 of the first pilot signal fp1are formed on one lateral side of the track as viewed in the track pathdirection (for example, on the right hand side in the direction ofrotation). Pits 53 of the second pilot signal fp2 are formed on theother side (left hand side) of the track. With respect to the adjacenttrack t₂, the pits 53 of the second pilot signal fp2 are formed on oneside (right hand side) as viewed in the track path direction at aposition corresponding to the horizontal blanking period during everyperiod H. On the other side (left hand side), the pits 52 of the firstpilot signal fp1 are formed. Thus, the positions at which the pits 52and the pits 53 of the first and second pilot signals fp1 and fp2 areformed are alternately reversed in the disc radial direction.

In addition, pits 54 of the third pilot signal fp3 are formed in theposition (V.BLK) corresponding to the vertical blanking period whichcoincides with the parts where the individual track turn designationnumbers change.

In the present embodiment of the invention, the pilot signal pits 52 and53 are formed at only the position H.BLK within one period H. They arenot formed at other parts 55, but the pits 52 and 53 may also be formedin these parts 55.

The part of the position H.BLK shown in FIG. 3B of the disc 50 is shownas being further enlarged in FIG. 4. The surface 56 of those parts ofthe disc 50, in which pits are not formed, is planar and does .Iadd.not.Iaddend.have a guide groove.

In the present embodiment of the invention, the pits 51 are formed sothat one of the edge lines of each track is substantially coincidentwith the nearest edge line of the adjacent track. That is, the adjacenttracks t₁, t₂, t₃, . . . are formed so that they are successivelycontiguous. Accordingly, the track pitch TP is substantially equal tothe track width TW. At central positions which are approximatelyintermediate between the centerlines of the mutually adjacent tracks,pilot signal pits 52 and 53 are formed with overlapping on two tracksadjacent each other.

FIG. 4 shows a reproducing stylus 60 tracing the recorded track on thedisc 50, having the above described pit arrangement. Only the bottomface 61 of the stylus 60 and the bottom face of an electrode 62 areshown. The bottom face 61 of the stylus has a part with a maximum widthSW, which is greater than the track pitch TP of the disc 50. Anelectrode 62 has a thickness of 500-3000 A and is fixed to the rear faceof the stylus at the rear edge of the bottom face 61. As the disc 50rotates in the arrow direction Y, the reproducing stylus 60 traces alongthe surface of the disc 50. The electrostatic capacitance between theelectrode 62 and an electroconductive layer covering the entire surfaceof the disc varies in response to the pits 51. The main informationsignal recorded by the pits 51 is reproduced.

At the same time, the pilot signals of frequencies fp1 and fp2 arerecorded by the pits 52 and 53 and are also reproduced by the electrode62. If the center of the electrode 62 deviates from the centerline ofthe .[.tradk.]. .Iadd.track.Iaddend., a level difference occurs in thereproduced pilot signals. A tracking servo operation is then carried outby a circuit described hereinafter.

Since the main information signal tracks comprise a series or successionof pits formed in substantially a contiguous state there is asubstantially uniform effect because of unnecessary light beam partsprojected onto the original disc by the recording apparatus.Furthermore, there are not spacing parts between adjacent tracks. Duringtracking and reproducing by the reproducing stylus 60, the bottom face61 of the stylus structure is in sliding contact with the disc surface,in a sustantially uniform state. The groove guiding phenomenon does notarise.

Since the adjacent tracks are contiguous to each other, the pit width(i.e., track width) can be set at a greater value if the track pitch isthe same as in the conventional case, whereby the S/N ratio becomesgreater. Alternatively, if the pit width is made the same as in theconventional case, the track pitch can be decreased, whereby therecording capacity is increased.

The reproducing stylus 60, has a shape as previously described in theaforecited applications, for example. The reproducing stylus 60 has anelectrode 62 of a construction such that the electrode width at thebottom face does not become very large even when the bottom face of theelectrode becomes worn. The life of the stylus is thus prolonged.

When the electrode 62 is directly over or covering the pits 52 and 53,variations in capacitance occur. But, capacitance variations occur andthe pilot signals are reproduced even when the electrode 52 is notdirectly over the pits 52 and 53.

An example of an apparatus for reproducing (playing) the above disc willnow be described with reference to FIG. 5. A motor 71 rotates therecorded disc 50 on turntable 72 at a rotational speed of 900 rpm. Thetrack on the disc 50 is traced by the reproducing stylus 60 which isfitted into a reproducing transducer 73. The reproducing stylus 60 picksup a reproduced signal as a minute variation of electrostaticcapacitance from the disc 50 and supplies the signal to a preamplifier74 having a resonant circuit. The resonant frequency varies in responseto this variation in electrostatic capacitance in order to form a signalof a desired level. The resulting output of the preamplifier 74 isdemodulated into the original information signal by a demodulator 75 andis sent out as an output through an output terminal 76.

The output signal of the pre-amplifier 74, is supplied to a low-passfilter 77, from which a pilot signal is obtained. The output signal ofthe low-pass filer 77 is supplied to an automatic gain control (AGC)circuit 78. The low-pass filter 77 removes a frequency modulatedinformation signal component so that the AGC circuit 78 will not operatein response to the main information signal component and takes out alow-frequency component including a pilot signal.

When, the contact between the reproducing stylus 60 and the disc 50fluctuates, the level of the reproduced signal fluctuates. However, theAGC circuit 78 operates to always maintain the specific levels of thepilot signals irrespective of such fluctuations of the reproduced signallevel. The reproduced levels of the first and second pilot signals fp1and fp2 vary in response to the tracking deviation of the reproducingstylus 60. Tracking control is carried out by detecting this variation.For this reason, if the AGC circuit were to cause the reproduced levelsof the two pilot signals to be constant, tracking control would not bepossible in response to the above mentioned detection output.Accordingly, the AGC circuit 78 is operated to always maintain the totalreproduced level of the pilot signals at a specific level.

The output signal of the AGC circuit 78 is supplied respectively toamplifiers 79, 80 and 81. Here, each of the amplifiers 79 and 80 is aband-pass amplifier. The amplifier 79 has a steep passing frequencycharacteristic at only the frequency fp1. The amplifier 80 has a steeppassing frequency characteristic at only the frequency fp2. The firstand second reference .Iadd.or pilot .Iaddend.signals fp1 and fp2 shownin FIGS. 7(A) and 7(B) are obtained separately from the amplifiers 79and 80, respectively. These signals pass through level adjustors 82 and83, where their levels are adjusted. The resulting signals are thensupplied to a gate switching circuit 84.

The amplifier 81 is a band-pass amplifier having a steep passingfrequency characteristic at only the frequency fp3, for enabling a thirdreference .Iadd.or pilot .Iaddend.signal fp3 to pass therethrough. Thereference signal, shown in FIG. 7(E), is obtained from the amplifier 81and supplied to a detecting circuit 86. The resulting output signal issupplied to operate a monostable multivibrator 87. The monostablemultivibrator 87 does not respond to noise components. The output signalthereof is derived from an output terminal 88.

In a normal reproducing mode, the output signal from the terminal 88 isapplied to trigger a flip-flop circuit (not shown). The output signal ofthe flip-flop circuit is a switching pulse applied, through an inputterminal 85, to a gate switching circuit 84. In a special reproducingmode (such as still picture reproducing mode) or slow motion picturereproducing mode, the signal from the terminal 88 is applied to akick-back pulse forming circuit (not shown) whose output kick-back pulseis applied to a terminal 100.

The gate switching circuit 84 switches the pilot signal fp1 and fp2every revolution period of the disc 50 in response to the switchingpulse supplied through the terminal 85. The disc rotational speed in thepresent embodiment of the invention is 900 rpm. Therefore, two frames ofthe video signal are recorded for each revolution of the disc 50. As aresult, a switching pulse inverts polarity every two frames (1/15second). The gate switching circuit 84 supplies a signal as indicated inFIG. 7(C) and a signal as indicated in FIG. 7(D), respectively, todetecting circuits 90 and 91.

The detecting circuits 90 and 91 detect the envelopes of theirrespective input reference .Iadd.or pilot .Iaddend.signals and convertthe envelopes into DC voltages. These voltages are then supplied to theinput terminals of a differential amplifier 92. This differentialamplifier 92 compares the output signals of the two detecting circuits90 and 91 which vary in response to the reproduced levels of thereference .Iadd.or pilot .Iaddend.signals fp1 and fp2. This generates anoutput tracking error signal which indicates the tracking errordirection and quantity.

This output error signal passes through a variable resistor 93 foradjusting the loop gain of the entire servo loop and is supplied to aproportional compensation circuit 94 and to a differential compensationcircuit 95 of known circuits. The resulting signals are given a specificcharacteristic compensation in the compensation circuits 94 and 95 andare respectively passed through variable resistors 96 and 97 for gainadjustment. They are then supplied to a power amplifier 98, where thesignals are amplified to a specific power. The resulting output of thepower amplifier 98 is led out through an output terminal 99 and appliedto the tracking control mechanism of the reproducing transducer 73.

The reproducing transducer 73 has an arrangement as shown in FIG. 6, forexample. A cantilever 101 has a reproducing stylus 60 mounted at itsfree end. Its other end is connected via a damper 102 to a bracket 103.The electrode of the reproducing stylus 60 is connected through a verythin, slack, and flexible lead wire 104 to a terminal 106 on the supportplate 105. Except at its ends, a very thin gold wire 107 is bonded tothe cantilever 101 over a specific distance in the longitudinaldirection. The ends 107a and 107b lead wire are respectively connected,in a slackened state, to terminals 108a and 108b on the support plate105. A permanent magnet 109 is secured by way of a bracket 110 to thelower surface of the support plate 105. The wire 107 is thus disposed inthe strong magnetic field of the magnet 109.

The control signal from the output terminal 99 is applied across theterminals 108a and 108b. When the control signal current flows throughthe terminals 108a and 108b and the wire 107, a displacement force actson the wire 107. This force is in the transverse direction which isperpendicular to the longitudinal direction of the cantilever beam 101.The force is generated in response to the current in the wire 107,according to the Fleming's left-hand rule, since the wire 107 isdisposed within the magnetic field of the magnet 109. Since the wire 107is bonded to it, the cantilever 101 is displaced by the force acting onthe wire 107. As a result, the reproducing stylus 60 is displaced in adirection perpendicular to the longitudinal direction of the track.Tracking control is accomplished so that the reproducing stylus 60traces accurately along the track.

One embodiment of a specific AGC circuit 78 is shown in FIG 8. Theoutput signal of the low-pass filter 77 is supplied through an inputterminal 121 of the AGC circuit 78 and to an AGC amplifier 122. Theoutput of amplifier 122 is supplied through a coupling capacitor to anamplifier 123. The output signal of the amplifier 123 is led out throughan out terminal 124 and to the amplifiers 79, 80 and 81. The outputsignal of the amplifier 123 is also supplied to a detection circuit 125,where it is envelope detected and converted into a DC component. Theoutput of the detection circuit 125 is amplified in a DC amplifier 126and is converted into a DC voltage corresponding to the level of thereproduced signal. At potentiometer 127, a DC voltage level issuperimposed upon this output DC voltage. The DC level is fed back fromthe bias adjuster to control the gain of the AGC amplifier 122. As aresult, pilot signals fp1, fp2, and fp3 have constant levels when theyare led out through the output terminal 124.

The output of the differential amplifier 92 is a DC voltage used as atracking error signal. Therefore, it is apparent that the AGC circuit 84cannot be connected on the output side of the differential amplifier 92.Furthermore, an automatic gain control reference voltage cannot beobtained from this output side.

Next, examples of modification of the AGC circuit 78 will be describedwith reference to FIGS. 9 and 10, respectively. In FIGS. 9 and 10, thoseparts which are the same as corresponding parts in FIGS. 5 and 8 aredesignated by like reference numerals. Description of such parts will beomitted.

Referring first to FIG. 9, the output of the low-pass filter 77 isintroduced through the input terminal 121 and is supplied to the AGCamplifier 122. The .[.outputs of.]. .Iadd.detected outputs of thereference or pilot signals fp1 and fp2 from .Iaddend.the detectioncircuits 90 and 91 are supplied to the differential amplifier 92 and arepassed through resistors 131 and 132 to be added together. The resultingcombined signal is passed through a DC amplifier 133 and fed back as again control voltage to the AGC amplifier 122. .Iadd.As a result, thereference or pilot signals fp1 and fp2 are controlled such that thetotal level of the reference or pilot signals fp1 and fp2 is maintainedat a specific level. .Iaddend.

Referring to FIG. 10, the signal from the low-pass filter 77 isintroduced through an input terminal 141 and is supplied to amplifiers79, 80 and 81 and to a detector 142. The output DC voltage of thedetector 142 is amplified by an amplifier 143 and then applied as a gaincontrol voltage to AGC amplifiers 144 and 145. These AGC amplifiers 144and 145 carry out AGC operation from a DC level .Iadd.to control thelevels of the reference or pilot signals fp1 and fp2.Iaddend..

As a further modification of the embodiment shown in FIG 10, a circuitmay add outputs of the amplifiers 79 and 80 which are supplied to thedetecting circuit 142. In this case, the low-pass filter 77 may beomitted. Another AGC amplifier may be provided at the output side of theamplifier 81.

Next, operations in special reproducing modes, such as still picture andslow motion picture reproducing modes, will be explained. In the stillpicture reproducing mode, the reproducing transducer 73 stops moving ina radial direction across the disc 50. Then, the reproducing transducer73 repeatedly traces the same one track t₂, for example. In this case,there is a necessity for the reproducing stylus to trace the track t₂and an end portion thereof indicated by t₂, and then to again trace thetrack t₂ after passing the position V.BLK. However, if a polarityswitching operation of the gate switching circuit 84 merely ceases, whenthe reproducing stylus begins to trace the track t₃ after having tracedthe track t₂, the reproducing stylus jumps indefinitely to the track t₂or t₄ responsive to a detection of the pilot signals tp1 and fp2. Itdoes not necessarily follow that the reproducing stylus definitelytraces the track t₂ again.

Then, in the still picture reproducing mode, the gate switching circuit84 stops its polarity switching over operation. At the same time, thekick-back pulse obtained from the signal at the terminal 88 is applied,through the terminal 100, to a power amplifier 98 during the verticalblanking period. The signal from the terminal 88 is shaped into thekick-back pulse form shown in FIG. 11(B) which corresponds to two frameintervals of the video signal shown in FIG. 11(A).

Responsive to the kick-back pulse, the tracking control mechanism forthe reproducing stylus is kicked back and jumps from the track t_(2') tothe track t₂ at the position V.BLK. The polarity of the kick-back pulseis selected in consideration of a control polarity of the trackingcontrol system and mechanism. Besides, the amplitude and pulse width ofthe kick-back pulse is selected so that the kicked back reproducingstylus jumps one track pitch.

An operation of the slow motion picture reproduction is next described.If the slow motion picture reproduction ratio is 1/7, for example, thetransferring speed of the reproducing transducer 73 is redueced to 1/7in the radial direction along the disc 50. A kick-back pulse shown inFIG. 11(D) is obtained from the signal and, is applied to the terminal100. At the same time, the frequency of the switching pulse is dividedby 1/7 when supplied from the terminal 88 to the terminal 85, as shownin FIG. 11(C). The resulting pulse is supplied to the gate switchingcircuit 84 through the terminal 85. The slow motion of the picturereproduction is thus 1/7 of the original motion.

The reproducing stylus is transferred to the adjacent track afterrepeated reproduction of the same track of the predetermined number oftimes (seven times in this case). The polarity of the switching pulse tobe supplied to the gate switching circuit 84 during the verticalblanking period is reversed, while the kick-back pulse is not suppliedto the terminal 100.

The system of the present invention may be used not only for recordingand reproducing video signals but also for recording and reproducingaudio signals, and the like. A high dynamic range, with high quality, isavailable for recording video and audio signals with multichannels onthe same single track. The reproducing and tracking of this recordedinformation track is somewhat as described hereinbefore.

Further, this invention is not limited to these embodiments. Variationsand modifications may be made without departing from the scope of theinvention.

What is claimed is:
 1. A tracking control system in a reproducingapparatus having a transducer for reproducing signals recorded on arotary recording medium in which a main information signal has beenrecorded in a plurality of adjacent tracks, first and second referencesignals having different frequencies, each of said reference signalsbeing alternately recorded at intermediate positions betweenlongitudinal center lines of the adjacent tracks, and a third referencesignal being recorded at positions corresponding to a switching of thefirst and second reference signals, said first, second and thirdreference signals being in a frequency band which is lower than thefrequency band of the main information signal, said tracking controlapparatus comprising:means for controlling the reproducing transducer tocorrectly track along the main information signal track; a firstseparating means for filtering and separating a low frequency bandcomponent including at least the first, second and third referencesignals from the signal reproduced by the reproducing transducer; asecond separating means for separating the low frequency band componentinto the first, second and third reference signals; means for detectingthe separated first and second reference signals; means for selectivelyswitching the separated first and second reference signals responsive tothe separated third reference signal, said switched first and secondreference signals being applied to the detecting means; a control signalproducing means for producing a control signal in response to theoutputs of the detecting means and for applying the control signal tothe tracking control means; and automatic gain control means forbringing the .[.levels.]. .Iadd.total level .Iaddend.of .Iadd.at least.Iaddend.the separated first.[.,.]. .Iadd.and .Iaddend.second .[.andthird.]. reference signals to a predetermined level, said automatic gaincontrol means being in a signal transmission path between the firstseparating means and the control signal producing means.
 2. A trackingcontrol apparatus as claimed in claim 1 in which said automatic gaincontrol means comprises an amplifier means in the signal transmissionpath between the first separating means and the control signal producingmeans, and means for generating a gain control signal responsive to asignal appearing in the signal transmission path, the gain controlsignal being applied to the automatic gain control amplifier means.
 3. Atracking control apparatus as claimed in claim 1 in which said automaticgain control means is in a signal transmission path between the firstseparating means and the second separating means.
 4. A tracking controlapparatus as claimed in claim 3 in which said automatic gain controlmeans comprises an automatic gain control amplifier means which issupplied with the output signal of the first separating means, theoutput signal of said automatic gain control amplifier means beingsupplied to the second separating means, a detecting circuit means fordetecting the output of the automatic gain control amplifier means, andmeans for feeding back the output of the detecting circuit means as again control voltage to the automatic gain control amplifier means.
 5. Atracking control apparatus as claimed in claim 1 in which said automaticgain control means comprises an automatic gain control amplifier meanswhich is supplied with the output signal of the first separating means,the output signal of said automatic gain control amplifier means beingsupplied to the second separating means, and means for adding theoutputs of the detecting means and for feeding back the added signal asa control signal to the automatic gain control amplifier means.
 6. Atracking control apparatus as claimed in claim 1 in which said automaticgain control means comprises an automatic gain control amplifier meansin a signal transmission path between the detecting means and thecontrol signal producing means, and means for applying the output signalof the first separating means as a gain control voltage to the automaticgain control amplifier means.